Two types of forms are used to construct concrete work.
The first type is comprised of reusable forms that form a rigid watertight pocket that concrete is poured into.
Steel sheets attached to a bearing structure form the liner walls.
This type of form presents several disadvantages, including:                forms that are quite heavy in order to resist the hydrostatic forces,        the custom of using fast-set concretes whose resistance stresses exceed requirements, etc.        
In order to resolve these different problems, the second type of form appeared, namely expendable forms with filtering walls.
The concept of these filtering walls was developed to create different products (FR-A-2.675.181 et FR-A-2.647.839).
In particular, these filtering walls can be used to reduce the weight of forms.
The “form/filling” composite presents improved mechanical properties compared to a shell made by traditional means.
The first forms primarily used metal installed to create the desired permeability in the liner skin.
To create the liner skin on a form wall, several metal plates have to be installed to obtain the desired surface.
In addition, in these types of form, since part of the metal structure is not covered by a regulatory coating, it presents long-term durability risks.
Consequently, the structural calculations cannot take the metal structure into account.
In addition, the installed metal skin, even when protected against corrosion, can lead to damage due to corrosion phenomena.
In order to compensate for these disadvantages, there is an expendable form with a filtering skin (FR-A-2.800.109) that, in place of the installed metal, uses a mesh or fabric with wide panels obtained by interlacing warp and weft strands.
The size of the mesh panels is determined by the aggregates and desired filtering.
According to this solution, since the mesh is flexible when it is attached to the form's reinforcement, it is stretched in the two perpendicular directions to obtain uniform tension in the warp and weft strands in both directions.
In addition, spacers keep the liner skin away from the reinforcement.
The disadvantage of this type of form is that it over-consumes mesh and positions the mesh such that it hinders filling the form.
In effect, part of the mesh penetrates into the volume to be filled, which poses a problem.